Field of the Invention
The invention relates to a method for monitoring the functional capability of lambda sensors, in which switching times of the lambda sensor are measured.
In internal combustion engines, pollutant emissions can be reduced by catalytic post-treatment.
A prerequisite of catalytic post-treatment is a certain composition of the exhaust gas, which is known as a stoichiometric mixture. That purpose is served by mixture regulation by means of a so-called lambda sensor, by which the mixture composition is periodically regulated within close limits around a command or setpoint value. To that end, if the fuel/air mixture is rich, the sensor outputs a high voltage (the rich voltage), and if the fuel/air mixture is lean, it outputs a low voltage. A voltage jump that is characteristic for lambda=1 is located between those voltages.
The sensors may become defective in the course of operation, causing the mixture composition to be incorrectly regulated. In that case the exhaust gases are no longer correctly detoxified, and over the long term the catalyst is even damaged as a result.
It is therefore necessary to monitor the functional capability of the lambda sensor.